Alternating-current motor.



- I E. F. W; ALEXANDERSON.

-'ALTBRNATING CURRENT MOTOR;

APPLICATION FILED NOV; 9, 1905."

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PATENTED JAN. 15, 1907. 1

No. 841,610, PATENTED JAN.15, 1907.

' E. P. w. ALEXANDBRSON.

ALTERNATING OURRENT MOTOR.

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APPLIGATION FILED NOV 9,1905

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I AHLIOATION FILED NOV. 9. 1905..

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//7 1 6/760/' Ernst F. 1 14/14 e/mnde/ son A tty UNITED STATES rirrnxr oFFIoE.

ERNST F. W. ALEXANDERSON, OF SCHENECTADY, NEW YORK, ASSIGNOR TO GENERAL ELECTRIC COMPANY,

A CORPORATION OF NEW YORK.

ALTERNATlNG-CURRENT MOTOR.

Nan/841,610.

Specification of Letters Patent.

Patented Jan. 15, 1907.

Application filer. November 9, 1905. Serial 110.286.510-

To a]! whom if may (ION/7077b.

Be it known that I, ERNST F. W. ALEX- axnnnsox, a subject of the King of Sweden, residing at Schenectady, county of Schenectady, State of New York. have invented certa-in new and useful Improvements in Alterhating-Current Motors. or which the following is a specification.

My invention relates to alternating-current motors of the induction type: and one of its objects is to provide a novel arrangement of and method of control for such motors whereby a. plurality ol speeds may be obtained bearing any desired ratio to each other without the use of aspecial winding and with a smaller number of terminal connections than has been possible heretofore.

My invention in certain of its aspects is particularly applicable to motors adapted for operation on three-phase current: but in other of its aspects it is not limited to a motor 1 of any particuL-u' number ot phases nor even necessarily to a motor designed for operation at a plurality of speeds.

Certain special connections are now well known in the art by means of which a threephase induction-motor may be caused to 0perate at a plurality of diflerent speeds bearing a certain ratio to each other without employing a special type oi wmdlng. Such, tor mstance, is the connection shown in Patent No. 725,415, Dahlander and Lmdst'rom, winch shows'a simple connection of means by which two speedsof a. ratio of two' to one ed in either the first, second, or third phase. l for the other speed, and some ot the coils two speeds may have their terminal connec- 1 may be obtained. speed ratios are required, however, not obtainable with such a simple connection, it

has, been necessary heretofore to employ either a special winding designed with particular reference to the speed ratios required or else to employ a practically prohibitive number of terminal connections. For in-v stance, consider a standard three-phase winding which is to be connected for two ditferent speedsthat is, for two different polenumbers bearing any desired ratio to each other. the first phase for one speed may be con nectwhich are connect-ed similarly with respect to the phase in which they are placed tor the tions relatively reversed, so as to be travlvhen certain other 1 Obviously a coil that is connected in ersed by currents in relatively opposite directionsthat is, considering the coils which compose any one phase for one of the speeds it would be necessary to split those coils first into three groups, according as they are to be connected in the first. second,'0r third phase For the other speed. and then to split each of those three groups into two, so as to render it possible to reverse the current in a portion of the coils of each group relatively to the other coilsthat is, the coils of each phase must be divided into six groups. making eighteen groups in all. Each group requires two terminal connections. Consequently thirty-six terminal connections are required for connecting the motor for two different speeds. Obviously such a number of terminal connections may be prohibitive in practice. My invention in one of its aspects consists in connecting the windings of amotor supplied with three-phase current which is to operate at a plurality of speeds in T connection for both speeds instead of the ordinary three-phase connection, either deltaor Y, and in connecting together in agroup the coils which undergo similar changes in circuit'connections in shifting from one speed to the other. By employing the T connection the number or phases inside the motor is reduced,

I coils into their proper roups the number of necessary groups is reduced. .Thus, for instance, if the coils connected in one phase for either speed be considered it is obvious that g each coil must be either in that phase or in the other phase for the second s eed, and consequently it is necessary to ivide the coils of each phase into four groups only, making a total of eight groups and sixteen terminal connections. By properly arranging the groups in the T connection certain of them may be permanently connected to gether, reducing the number of external leads required to thirteen. Obviously a control which would be impracticable with thirty-six leads may easily be commercially possible when only sixteen or thirteen leads are required.

A peculiarity of the T connection as comi pared with other polyphase connections is the inequality in the number of coils in the It is well known in thcart that two phases. i when a T connection is employed"- l l i from three to two, so that in splitting up the" noivel method of arranging the connections nase operation in order to secure at proper alance of the bases the number of coils in one hasesho d bear to the number of coils in t e other phase a ratio approximately equal to the ratio of ,s i'xto seven'or, more accurately, .86.-

other words, the number of coils er"- ole for a T connection should be such t at it may be divided into two parts bearing to each other the ratio'of approximately siXP'Eto seven. Inother words, the

number of coils per pole must be divisible by a numbernot less than thirteen. Obviously a large number of .Iploles' isrequired the totalwnumber of coils w ch in' ordinary windings must a multiple not only of the number of coils-:per pole, but.also of the number poles may be very large, and when the motor isto operate at a lurality of speeds ireqm'm 'n" le-numbers w 'ch contain lar e fiactors are primeto each other the nurhiren-ofcoils required may clearly become so large as to be out of the question. For in- ;stanee,. with windings as ordinarily arranged imonrlier to obtain'a balanced T connection bethan ei ht-pole and a tenole windinga: totalnum er of coils would ave to be employed divisible by eight, by ten, and by thirteen Such a number of coils in a small gagmotor. would be out of the question.

One feature of my invention consists in a I eta motor in: which the number of coils is not quired connecting the winding in the ordiv 9pm manner, is nevertheless not limited to :r-T connection or to a threehase motor nor given to a multispeedmotor, ut may be employed wherever it is desired to connect a for a given number of poles and phaseswhen the number of COIlS divided by file-number of poles gives a number which is met divisible in the proper proportion betweenthe phases. My invention in this aspect consists in divid ng the total number of coils between the phases in proper proportion, then dividing the number of coils for each. phaseby the number of poles, from which-latter division there will be a number of coils left over, and distributing these remaining coils as uniformly as possible a portion of the poles. A W'lIldlIlg (la in this manner will have an excess an or de iency of acoil at some of'the poles;

but this excesso'r deficiency does not injure the efficiency motor to any extent and.

renders it possible to obtain a complete alance between the phases with respect to the total number of coils per phase- My invention further comprises an alter nating current motor with a distributed windin having a number of coils in a phase, which ivided y the number of oles gives a fractional number, the poles o the phase being formed some of a greater and some of a lbess number of coils than said fractional num- My invention further'comprises the combination, with an alternating-current motor having its primary winding connected in a plurality of coil groups, of means for establishing a plurality'of T connections of said winding with the groups arranged in varying relations to each other, the groups being arranged to produce different pole-numbers when their relative connections to each other are varied.

My invention will best be understood by reference to the accompanying drawings, in which Figure 1 shows diagrammatically the circuit connections of a motor arranged to operate with three-phase current at a'plurality of speeds in accordance with my invention. Figs. 2 and 3 show the connections of the motor-winding established by the controllingswitch of Fig. 1. Fig. 4 is an explanatory diagram showing the method by which the coils are selected for the several groups, and

Fig.5 shows a development on a plane surface of a portion of the motor-winding arvIIO tive connections of which to each other are letters0ne a capital and one a small letter connection, but that the positions of the groups in the two arrangements are different.

Each group is provided with two referenceand with a positive or negative sign. Thus, for

instance, one group is provided with the refer-- ence characterAa In Fig. 2 all the groups having the reference-letter a are connected in one phase, while the groups having the reference-letter b are connected in the other phase. In Fig. 3 all thegroups having the referenceletter A are connected in one phase, while the groups; having the reference-letter B are--c0nnected in the other phase; "Furthermore,

the groups having a positive sign have the same relative terminal connections with re spect to the direction of current-flow in both arrangements, while the groups having the 'negative sign have their terminal connections relatively reversed in the two arrangements.

The purpose "of this notation is as follows: Consider the several groups in Fig. 3 in the phase indicated by A. Reference-letter A signifies that all these groups are connected in'gthis. phase for this speed. As has been pointed out before, it is obvious that some of these groups will be connected in the same phase for the other speed, while others of the groups will be connected in the other phase. The'groups which are to remain in the same phase are provided with reference-letter a, while the groups which are to be connected in the other phase for the other speed are pro vided with the reference-letter I). Also, as has been heretofore pointed out, the relative direction of currenteflowin some of the groups will be reversed in changing from one speed to another. Consequently the positive and negative signs are employed to indicate the relative reversal of connection. The plus- :bigns mean that the groups to which they are applied are to have the same relative connections for both speeds with respect to direction of current-flow, while the minuss'igns mean that the relative direction of current flow is to be reversed to those groups in changing from one speed to another. ,for instance, both groups Ac+ and Aawill be in the same phase for both speeds; but the terminal connections of the group Aa will Thus,

be relatively reversed for the two speeds.

Tlhisis clearly shown by comparison of Figs.

2 and 3, observing the group terminals which are given corresponding numbers of reference in the two figures. W 1th this prelimi- \nary explanation the diagram Fig. 4, illusder to simplify the diagram as much aspossible, a coil is indicated by a single arrow representing by its position thecentral hne of the coil'and the direction of the arrow representin the direction of current-flow in the coil. Ior instance, an arrow pointing upward may be considered as representing the I center line of a coil in which the current is fiowingin a counter-clockwise direction at any given instant, while an arrow pointing downward indicates the center line of the coil in which the current at the same instant is flowing in a clockwise direction.

Uponinspecting the arrows in the rows A and B it will be seen that they are ar 'anged 1n unequal groups. Thus the row A is arranged in four groups in which the arrows number, respectively,.6, 6, 6, and 7, while the arrows in row B are in four groups which number, respectively, 7, 8, 7, and 7. Similarly, the arrows in row a are in six groups, which number, respectively, 4, l, 4, 5, 4, and 4, while the groups of arrows in row I) num her 5', 5, 4, 5, 5, and 5, respectively. The reason for this irregularity in the groups will be evident from the following considerations: The diagram represents a winding having fifty-four coils, which must ,be connected both for four poles and for six poles in T connection. Considering first the six-pole con nection, fifty-four coils with six poles gives nine coils per pole, and the number 9 is not divisible in the proper ratio for a T connection. The closest approximation to the proper ratio that can be obtained with nine coils is four to five, or .80, which is too small, since .86 is desired. With the four-pole con nection the situation is still worse, since the total number of coils is not evenly divisible by the total number ofthe poles. Conse quently with the symmetrical connections that have been employed heretofore it would impossible to connect the winding in question as .ilesi in the present case. I accon'iplish the desired result, however, in the fol lowing manner: Instead of attempting to number of poles required I first assign the total number of coils in proper proportion between the two phases. Fifty-four may be divided into twenty-five and twenty-nine, which gives a ratio of .86, which is exactly what is required for the proper phase balance with the T connection. I then take the twenty-live coils which have been assigned to one phase and divide them among the four poles in the first case and among the six poles in the second. In each case one coil remains after an equal division, and this one coil I connect in any one of the poles. When dividing the twenty-nine coils among the four poles, there is similarly an excess of one, which excess coil is connected in a pole of the B phase, which is preferably displaced a maximum amount from the excess-coil pole in the A phase, so that the angular relation of the poles is maintained as uniform as pos-. sible. In dividing the twenty-nine coils among the six poles for the second speed there is deficit of one coil instead of an excess, so I forin onecoil with only four poles instead of five, and preferably place this pole adjacent to the pole in the a phase having an excess of one coil. In this manner the proper angular positions of the poles are exactly maintained. By the method outlined above divide the fifty-four coils evenly among the with only fifty-four coils I obtain T connec tions for two diiierent pole-numbers with the phases exactly balanced.

Having thus determined the connect-ions l l t t of the coils with respect to the poles of both responding arrows having the same direction.

represented thereby are to be connected in. the same phase for both speeds and that the relative direction of current remains the motor is shown in Fig. 5, in which full coils take the place ofthe arrows in Fig. 4, and the coils are shown superposed in the way they would be arranged in practice instead of with the coils of the two phases separated, as in Fig. 4. The coils of each group are provided with reference-letters corresponding to the reference-letters of Fig. 4, and the portion of the winding shown in Fig. 5 includes the first thirty-one coils, commencing at the loft in Fig.4. In choosing the coilpitch it is only necessary to select a width Since the presence of these arrows in I both the rows A and a means that the coils same for both speeds all the coils corre-F sponding to the lines in the row Ac+, may

be connected together in series. care being taken to secure the proper relative direction of current 1n the coils of the group. This may be taken care of by properly connecting the coils. Thus I have indicated diagrammat- I ically in the line Art-{- that the first four coils, beginning at the left, have open-end connections, while the remaining two coils have crossed or closed connections. reason for this is that the latter coils are indicated in the rows A and a by downwardlypOinting arrows, while the others are indicated byupwardly-pointing arrows, showing a current-flow in the opposite direction. I next proceed to form the row Aa', selecting the lines which are common to the rows A and a, but in which the arrows point in opposite directions. This opposite direction means that the relative-current-flow in these coils will be different for the two speeds. In. determining the question of open or closed connections for each coil in this group I have followed the direction of the arrows in row A. Consequently in the four-pole connection the terminal 3 of group Aa will be connected to terminal 2 of group Aa+.

while for the six-pole connection the terminal 4 will be connected to terminal 2. This corresponds to the connections shown'in Figs. 2 and 3, which show the six-pole and the four-pole connections of the groups, respec tively. The other groups Al)+, Ab, &c., are now selected in the manner that has been already explained, and since all possible combinations are represented by the eight groups all the coils will be. included in one group or another. It. only remains in establishing the proper connections for the two The I for the coil which will be suitable for-both pole numbers] with fifty-four slots the pole-pitch for the four-pole connection will be thirteen and one-half slots and for the sixpole connection nine slots. This latter number of slots gives a satisfactory coil-pitch for both numbers of poles and has been chosen for illustration in Fig. 5. Any other suitable coil-pitchsuch, for instance, as 1 might have been selected instead.

Although for the purpose of giving a complete explanation of my method I have described its application to a motor having two speeds in a specific ratio obtained by specific speeds to have regard to connecting the} proper group terminals to each other. These connections are shown for all the groups in Figs. 2 and 3, and in Fig. a control-switch C is shown with contacts adapted to make the proper connections or" the groups, as shown;

A portion of the complete winding of the i i i l pole-munbers, it is obvious that my invention is of general application, and in the aspect which relates to employing a T connecticn to minimize the number of leads it is applicable to any motor which it is desired to operate on three-phase current at different speeds, and, further, as regards the method by which I secure a proper balance of the phases with a number of coils not adapted to that end with the ordinary arrangement my invention is not limited to three-phase motors, nor even to multi-speed motors, although for single-speed two or three phase motors the number of coils can ordinarily be so chosen as to render the application of my invention unnecessary. For polyphase motors in general, however, where a number of speeds is required, and particularly in T-connected motors, whether arranged. for one or two speeds, my invention is particularly useful.

W'hat I claim as new, and

L 1. The method of connecting for a given number of poles and phases a winding formed of a number of coils not a common multiple of the number of poles and the desired number of coils per pole, which consists in assigning the proper proportion of the total number of coils to each phase, dividing the number of coils for each phase by the number-of poles, and dist-ributii'ig the coils forming the i remainder from said division among the poles of that phase, so as to utilize all the,

desire to secure i by Letters Patent of the United States, 1s

coils and to approximate the desired number of coils per pole. J y

2. The method of connecting for a given number of poles and phases a winding formed of a number of coils not a common multiple of the number of poles and the desired num- I ber of coils per po e, which consists in assign- I 1 mg the proper proportion of tne total num ber of coils to each phase, and distributing 5 ithecoils for each phase as uniformly as po sible among the several poles of that phase, so as to utilize all the coils.

. proximate said fractional number at each pole.

4. The method of forming a T connection of a given numberof poles with a winding which divided by the number of poles gives a number not divisible in the proper ratio for a T. connection, which consists in dividing the total number of coils into two sets bearing to each other approximately the proper ratio for a T connection in respect to number of coils and distributing each set as uniformly as possible among the several'poles.

5. The method of operating at a plurality of speeds a motor supplied with three-phase currents, which, consists in selecting the proper-coils for making a T connection for each number of poles corresponding to a desired speed, connecting 111 groups the C(JllS' which undergo similar changes in circuit connections in shifting from one number of poles to another, and varying the connections of said groups to obtain thedesired speeds.

6. The method of operating at a plurality of speeds a motor supplied with three-phase currents, which consists n selecting the proper coils for making a T connection for each number of poles corresponding to a de sired speed, and varying the connections of said coils to produce the proper T connections for the desired speeds.

' 7. In a dynamo-electric machine, a dis tributed winding having a number of coils in a phase which, divided by the number of poles gives a quotient having a remainder, the coils forming the remainder being distributed amonga portion of said poles and all the coils being connected in circuit.

8. In a dynamo-electric machine, a distributed winding having a number of coils in a phase which divided by the number of poles gives a fractional number, the poles of the phase being formed some of a greater and some of a less number of coils than saidv fractional number. i

9. In a dynamo-electric machine, a distributed winding arranged in T connection and formed of a number of coils which divided by the number of poles gives a number not divisible in the proper ratio for a T connection, the total number of coils being divided into two sets bearing to each other approximately the proper ratio for a T connection in respect to number of coils, and each set being distributed as uniformly as possible among the several poles.

10. In combination with an alternatingcurrent motor, means for establishing a plurality of T connections of the motor-windings with different pole-numbers, the coils which undergo similar changes in circuit connections in shifting from one number of poles to another being permanently connected in group.

11. In combination with an alternatingcurrent motor-having its primary Winding connected in a plurality of coil groups, means for establishing a plurality of T connections of said winding with the groups arranged in varying relations to each other, said grou s being arranged to produce different p0 enumbers when their relative connections to each other are varied.

In witness whereof I have hereunto set my hand this 8th day of November, 1905.

i ERNST F. W. ALEXANDERSON.

/Vitnesses:

BENJAMIN B. HULL, MARGARET E. WOOLLEY. 

